It is known that in the process of film formation aqueous coating systems are highly sensitive to extraneous substances present in the paint material, or on the substrate to be painted. This sensitivity becomes manifest in the formation of craters, dents, and similar surface defects. In primers this sensitivity can be eliminated or at least reduced by increasing the proportion of pigment. In many cases, however, especially in decorative finishes, this solution is not possible since it leads to a reduction in resistance characteristics and to an impairment of optical properties.
The sensitivity of aqueous coating systems to surface defects can also be diminished by the addition of surfactants. Because the additives are substantially incompatible with the paint material, the concentration of the additives in the region of the paint surface is frequently excessive, resulting in impaired intercoat adhesion, i.e., adhesion of subsequent paint coats. In order to avoid extreme incompatibility, it is the current practice in paints based on water-soluble binders containing carboxylate groups, to use polymeric additives which are copolymers of acid monomers and neutral ester monomers, principally (meth)acrylate monomers. By an appropriate adjustment of the acid component it is possible to achieve an optimum system efficiency. Even with such adjustment, there is considerable sensitivity to an excess of additives which leads directly to the adhesion problems described. In addition, the need for higher proportions of acid components detrimentally affects the properties of the paints and paint binders, such as their dilutability, viscosity or compatibility, and the hydrophilic and hydrophobic balance.